In many cases the permeability of biomembranes or model membrane systems can be related to overall membrane structure or to conformational properties of individual membrane constituents. The study of this relation requires the development of techniques for determining molecular conformation in membrane environments and the application of these techniques to systems likely to display membrane structure -- function relationships. C13 nuclear magnetic resonance offers great potential as a technique for conformational analysis in membrane systems. It has a number of structure dependent parameters and gives membrane spectra of sufficient quality to make accurate determination of these parameters feasible. We are therefore directing out attention at the utilization of one parameter, C13 chemical shift, for specific carbons in membrane fatty acyl chains in the hope of relating this to alteration in internal membrane structure. A number of structure and permeability altering agents will be used in an attempt to lay the ground work for a molecular description of permeability properties. The Polyene antibiotics are among the agents known to alter membrane permeability, and although their mechanism of action has not yet been firmly linked to a general alteration of membrane structure there is some evidence for such an effect. C13 studies of a polyene-perturbed membrane system should yield a more definitive description of their mode of action.